Disable LongTasksAPI on Github CI (#53009)

Summary:
Pull Request resolved: #53009

Changelog: [internal]

This disables the test for LongTasks API on Github CI as the execution speed there is unreliable and makes the current tests flaky.

This happens because the test is timing dependent, but the alternative would be to mock some core behaviors that I think might be even worse.

Reviewed By: cortinico

Differential Revision: D79510480

fbshipit-source-id: 277e42e36aa6dfebf4745d094541a667f58a0996

Author: rubennorte

packages/react-native/src/private/webapis/performance/__tests__/LongTasksAPI-itest.js

@@ -42,6 +42,16 @@ function ensurePerformanceLongTaskTiming(
 
 let observer: ?PerformanceObserver;
 
+const constants = Fantom.getConstants();
+const isGithubCI = constants.isOSS && constants.isRunningFromCI;
+
+// Skip the test on Github CI.
+// In that environment, execution speed is unreliable so some of the tasks
+// we schedule as part of the test run (even the task to report long tasks) are
+// also being reported as long, and we don't have a way to distinguish those
+// from the intentionally long tasks we're scheduling for testing.
+const describe = isGithubCI ? global.describe.skip : global.describe;
+
 describe('LongTasks API', () => {
   afterEach(() => {
     if (observer) {